What is the word or phrase that describes a traumatic event that stops or changes a person’s mode of living?

Something like an illness or something like happened to Tom Hanks in the movie Cast Away. Or even Tom Hanks’s girlfriend, who was going to school to get her doctorate but “put everything on hold” when Chuck (Tom Hanks’s character) disappears in a plane crash.

I’m almost looking for a psychological term here, and I want to study more about the topic, but I don’t have a term or phrase for it that I can use to research it.

Homes and Rahe, who developed the scale that grades stressful events, actually called these life-changing events.
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JLGJan 6 '13 at 16:11

@JLG Wow! That's just what I needed! Thank you! Why don't they teach kids about this scale in school? It seems it would make their lives ALOT easier if they understood it.
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leeand00Jan 6 '13 at 21:42

Is there a name for a question that inadvertently embeds the answer? The two most appropriate terms are trauma and life-changing event, both right there in the title. Trauma is relevant in the context from the psychological/psychiatric point of view, while life-changing event is significant from the social psychology aspect.
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KrisJan 7 '13 at 14:45

IMO, your use of life-changing experience and trauma are eminently suitable. I think that the medical term is simply psychological trauma. There appear to be different types of psychological trauma including situational trauma, physical trauma, childhood trauma, and possibly others.

+1 trauma is itself significant. It is relevant in the context from the psychological/psychiatric point of view, while life-changing event is significant from the social psychology aspect.
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KrisJan 7 '13 at 14:41

An Epochal event is one that has far-reaching implications in one's life. The free dictionary lists momentous as a synonym, so a momentous event is again a happening or a circumstance with the capacity to alter the course of one's life.

Earthshaking, or earth-shattering/world-shattering may be the best fit for what you are describing, as they carry a negative connotation, unlike pivotal, consequential, momentous, critical, or another potentially relevant synonym.

Although it's not used exclusively by psychologists and psychiatrists, a watershed moment is appropriate as well as most of the other suggestions made. If you do a Google search for watershed moment, you'll find psychological usages in many of the hits.

But OP also mentioned about what happened to Chuck's girlfriend in Cast Away, which was in effect due to the stress she was put into, which in all probability could be defined as either Acute Stress Disorder or PTSD(both psychologically).
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MohitJan 5 '13 at 5:28